<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>区域</title>
  <style>
    .btn {
      width: 100px;
      height: 50px;
      background: red;
      position: relative;
    }

    .btn:hover {
      background: blue;
    }

    .btn::before {
      content: "";
      position: absolute;
      top: -10px;
      right: -10px;
      bottom: -10px;
      left: -10px;
    }
  </style>
</head>

<body>
  <div class="btn">123</div>
</body>

</html>